NASA engineers found no electronic flaws in Toyota vehicles capable of producing the large throttle openings required to create dangerous high speed unintended acceleration incidents. The two mechanical safety defects identified by NHTSA more than a year ago - sticking pedals and entrapment by flaw mats - remain the only known causes for the acceleration incidents.

NHTSA will propose rules by the end of the year to require brake override systems, to require the standardization of keyless ignition systems and to require event data recorders in all passenger vehicles.

The National Academy of Sciences is expected to finalize its broad review of other cars by the end of the year.

"Today we can say clearly and affirmatively that NHTSA, America's traffic safety organization, was right all along," Transportation Secretary Ray LaHood said.

Toyota has maintained since the acceleration problems arose that there were no electronics defects and that the massive recalls for the mechanical defects fully addressed the problem.

In light of the government's findings, Toyota issued a statement from its chief quality officer in the U.S., Steve St. Angelo:

We believe this rigorous scientific analysis by some of America's foremost engineers should further reinforce confidence in the safety of Toyota and Lexus vehicles. We hope this important study will help put to rest unsupported speculation about Toyota's (electronic control system), which is well-designed and well-tested to ensure that a real world, uncommanded acceleration of the vehicle cannot occur.

Now the report by Department of Transportation officials, with help from NASA engineers, officially supports that position.

"We enlisted the best and brightest engineers to study Toyota's electronics systems, and the verdict is in. There is no electronic-based cause for unintended acceleration in Toyotas," LaHood said in a statement.

Toyota has recalled about 6 million vehicles globally since December 2009 for one or both of the mechanical defects that could lead to unintended acceleration. A series of other recalls -- 15 in 2010 alone -- boosted its overall recalled vehicles to more than 11 million in a little more than a year. Toyota paid the U.S. government three maximum fines totaling $48.8 million for delays in its recalls.

All that has put a huge dent in the company's image for quality and dependability. And that has taken a toll on sales -- starting with the initial recalls, when Toyota was forced to briefly halt all sales of eight models. The company was the only major automaker to post a U.S. sales decline last year, as the rest of the industry began a sales recovery from the recession here.

LaHood said NASA engineers "rigorously examined" nine Toyotas driven by consumers who complained of unintended acceleration. Investigators also reviewed 280,000 lines of software code for flaws, tested mechanical components and bombarded vehicles with electro-magnetic radiation to see if that could cause vehicle electronics to malfunction. A preliminary review of vehicle data recorders, released last August, also found no flaws.

In Tokyo on Tuesday, Toyota reported a 39% slide in quarterly profit but raised its full-year forecasts, thanks to booming sales in emerging markets in Asia, Africa and South America, even while its key U.S. market continues to be difficult.

In other moves to try to reassure customers -- in addition to the recalls -- Toyota began installing brake override systems on new vehicles that cut the throttle if the driver presses the brake and accelerator at the same time. It also created special teams to examine vehicles consumers complained about and appointed a chief quality officer for North America. The photo above is of a demonstration the company put on in San Diego last March to show Toyotas had no acceleration defects beyond the recall problems.

The study follows allegations by consumer advocates and safety groups that flawed electronics could be behind unintended acceleration in the Toyotas.

NHTSA has 3,000 complaints of sudden acceleration involving Toyota vehicles in the past decade, including 93 deaths. NHTSA, however, has confirmed just five of them.

Toyota's safety issues began receiving broad attention from the government after four people -- an off-duty California highway patrolman and his family -- were killed in a high-speed crash involving a runaway Lexus near San Diego in August 2009, and the huge recalls followed within months. It was later determined that an incorrect and unsecured floor mat caused the incident.

The National Academy of Sciences' separate study of unintended acceleration in cars and trucks across all companies is due out this fall.

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About Chris Woodyard

Chris Woodyard is an auto writer for USA TODAY who covers all aspects of motoring. He revels in the exhaust note of a Maserati and the sharp creases of a Cadillac CTS. Chris strives to live a Porsche life on a Scion budget. More about Chris